package com.tianjs.current.lock;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

/**
 * 独占式的获取锁
 * 同一时间只有一个线程获取到锁
 * @author admin
 */
public class Mutex implements Lock {
	//静态内部类，自定义同步器,继承队列同步器
	private static class Sync extends AbstractQueuedSynchronizer{
		private static final long serialVersionUID = 7789592229236578390L;
		//是否处于占用状态
		protected boolean isHoldExclusively() {
			return getState() == 1;
		}
		//当状态为0的时候获取锁
		public boolean tryAcquire(int acquires) {
			if(compareAndSetState(0, 1)) {
				setExclusiveOwnerThread(Thread.currentThread());
				return true;
			}
			return false;
		}
		//释放锁，讲状态置为0
		protected boolean tryRelease(int releases) {
			if(getState() == 0) {
				throw new IllegalMonitorStateException();
			}
			setExclusiveOwnerThread(null);
			setState(0);
			return true;
		}
		//返回一个Condition,每个condition都包含一个condition队列
		Condition newCondtion() {
			return new ConditionObject();
		}
	}
	
	//将操作代理到sync
	private final Sync sync = new Sync();

	@Override
	public void lock() {
		sync.acquire(1);
	}

	@Override
	public void lockInterruptibly() throws InterruptedException {
		sync.acquireInterruptibly(1);
	}

	@Override
	public boolean tryLock() {
		return sync.tryAcquire(1);
	}

	@Override
	public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
		return sync.tryAcquireNanos(1, unit.toNanos(time));
	}

	@Override
	public void unlock() {
		sync.release(1);
	}

	@Override
	public Condition newCondition() {
		return sync.newCondtion();
	}
	
	public boolean isLocked() {
		return sync.isHoldExclusively();
	}
	
	public boolean hasQueuedThreads() {
		return sync.hasQueuedThreads();
	}
}
